1. Field of the Invention
The present invention relates to a method for grouping multiple transmission antennas to increase communication capacity in a mobile communication system which includes multiple transmission antennas and multiple reception antennas.
2. Description of the Related Art
Conventional mobile communication systems have been developed mainly for voice transmission with a channel coding technique used to overcome the deterioration of channels in a radio environment. However, current mobile communication systems do not have the capacity to transmit high quality multimedia in addition to voice. As a result, current channel coding schemes that need to transmit more and more data in the same amount of data are pushed to operational limits and cannot satisfy the need for greater data transmission at a lower error rate. Faster data transmission in a forward link is particularly important when there is a rapid increase in the amount of data requested.
Many studies have been conducted to find ways of increasing communication capacity in mobile communication systems and enable faster data transmission. As a result, a multi-input multi-output (MIMO) technique using multiple transmission/reception antennas was established. According to the MIMO scheme, each transmitter and receiver in a network includes multiple antennas to transmit different data to and from each other.
With regard to the MIMO scheme, a construction of a transmitter according to a spatial multiplexing scheme will be described with reference to FIG. 1A, and then a construction of a transmitter according to a beamforming scheme will be described with reference to FIG. 1B.
FIG. 1A is a block diagram illustrating a transmission construction of a transmitter according to the conventional spatial multiplexing scheme.
According to the spatial multiplexing scheme, as shown in FIG. 1A, a transmitter 10 including a plurality of transmission antennas 11, 12, 13, and 14 each simultaneously transmit different symbols S1, S2, S3, . . . SN. That is, the transmission antenna 11 transmits symbol S1, the transmission antenna 12 transmits symbol S2, the transmission antenna 13 transmits symbol S3, and the transmission antenna 14 transmits symbol SN. Since the spatial multiplexing scheme transmits different symbols through multiple transmission antennas, it has a larger communication capacity than those of other MIMO schemes.
However, in general, the spatial multiplexing scheme is limited because the number of antennas for a transmitter must be smaller than the number of antennas for a receiver. This is because the receiver 20 uses a nulling and canceling detection scheme in connection with the application of the spatial multiplexing scheme. That is, in connection with the application of the spatial multiplexing scheme, it is possible that the receiver 20 performs low-complexity detection for the transmitted symbols only when the number of antennas for the receiver 20 is larger than that for the transmitter 10.
In contrast, in an actual mobile communication environment, the transmitter (i.e., base station) 10 has more antennas 11, 12, 13, and 14 than the receiver (i.e., mobile terminal) 20.
Therefore, when a base station using the spatial multiplexing scheme transmits data via a forward link, there is a limitation in the whole communication capacity of the mobile communication system due to the limited number of reception antennas of the mobile terminal, so that it is difficult to realize a transmitter according to the spatial multiplexing scheme.
FIG. 1B is a block diagram schematically illustrating the construction of a transmitter with a beamforming scheme in a mobile communication system. According to the beamforming scheme, a transmitter 30 including a plurality of antennas 31, 32, 33, and 34, multiplies a plurality of the same symbols S1 by different weight values W1, W2, W3, . . . WN, and then transmits the symbols S1 at the same time so that a receiver 40 may perform optimally.
In this case, there is an advantage in that a mobile terminal has good receiving performance of a symbol transmitted from a base station. But there is a disadvantage in that frequency efficiency is deteriorated because the same symbols (S1) are simultaneously transmitted through a plurality of antennas. That is, the beamforming scheme has reduced communication capacity. Therefore, a transmission construction according to the above-mentioned beamforming scheme may deteriorate communication capacity of the next-generation mobile communication system, which will actually require faster data transmission rates.